1. Field of the Invention
The present invention relates to an image contrast control technology. More particularly, the present invention relates to a contrast control apparatus and a method thereof, capable of being applied in the display device, so as to control the contrast effect of the image.
2. Description of Related Art
It is quite an important topic in improving images to enhance the image contrast. The images with a low contrast are mainly improved, for example, in which the difference between the image object and the background brightness is increased in the image. In terms of improving the image contrast, many methods have been developed in the conventional art. The conventional art mostly focuses on enhancing the image itself, but it ignores that the image is finally received by the viewer through the display device and the quality of the image is shown through the display device. However, due to some characteristics of the display device, the input image cannot be truly presented. Therefore, some methods for enhancing the image contrast through controlling the display device have been developed later on. However, the property of the image is ignored, or the mutual relationship between the image property and the display device characteristics is ignored, such that it is impossible for images with various different properties to achieve the effect of enhancing the contrast.
For example, as for a liquid crystal display (LCD) with a cold cathode tube as the backlight source, due to the limitation of the physical characteristics, it is impossible to display a full blackness in the black image. If the conventional method is used, the contrast of certain images cannot be enhanced, and what's worse, the image quality is deteriorated.
FIG. 1 shows a backlight source control architecture of a conventional display device. The display devices generated by different technologies have unique display characteristics. For example, as for the LCD with the cold cathode tube as the backlight source, it is difficult for the backlight source formed by the cold cathode tubes to be quickly switched on or off. As a result, the backlight source is always in the status of being lighted on. In order to obtain the total dark frame, the lights emitted by the backlight source must be completely blocked by the liquid crystal module. However, in terms of the physical characteristics, it is impossible for the elements to satisfy the requirement of completely blocking the light source. That is, the light leakage usually occurs. Therefore, in order to enhance the image contrast, it is necessary to consider the characteristics of the display device. As disclosed in Japan Patent No. 8-201812, mainly, when the average brightness of the image frame is relatively low, the brightness of the backlight source for the display device is enhanced, and the above factors are not considered, so that the dark part of the image is distorted. In addition, as disclosed in U.S. Pat. No. 7,053,881, the strength of the backlight source for the display device is controlled through the average value of the brightness of the image frame and the data concentration degrees. Although the data concentration information is used on purpose in order to solve the above problem, the enhancement of the image contrast achieved by separately adjusting the backlight source is very limited, and the image distortion still occurs.
FIG. 1 shows a backlight source control architecture of a conventional display device. As shown in FIG. 1, the image data are simultaneously input into a display control unit 100, an average brightness detecting unit 102, and a data concentration detecting unit 104, which are respectively directed to different functional processing. Next, the display control unit 100 directly outputs the data to the display device 108, without adjusting the data. In addition, the outputs of the average brightness detecting unit 102 and the data concentration detecting unit 104 are received by the backlight source control unit to determine the brightness to be changed. Then, a control signal is output to the backlight source module of the display device 108.
The above mentioned methods enhance the contrast merely by adjusting the strength of the backlight source, so the distortion still occurs. Therefore, those skilled in the art are still searching for new technologies capable of more effectively enhancing the contrast effect and further reducing the image distortion.